Film

Abstract

The present specification describes a bilayer electrolyte membrane comprising: a first layer comprising a polymer electrolyte having particles of a composite catalyst dispersed therein; and a second layer comprising a polymer electrolyte without any composite catalyst dispersed therein; wherein the thickness of the double-layer electrolyte membrane is 40m to 60m; the concentration of the composite catalyst in the first layer is 1 g / cm < 2 >-100 g / cm < 2 >; and the bilayer electrolyte membrane is a single adhesive polymer membrane. Also described are a method for preparing the bilayer electrolyte membrane, a catalyst-coated film for an electrochemical device comprising the bilayer electrolyte membrane, and a fuel cell comprising the catalyst-coated film.

Description

Technical Field

[0001] This invention relates to electrolyte membranes, their use in electrochemical devices such as water electrolyzers, and includes catalyst-coated membranes (CCMs) incorporating such membranes, as well as methods for their manufacture. Background Technology

[0002] Water electrolysis can be performed in both alkaline and acidic electrolyte systems to produce high-purity hydrogen and oxygen. Suitablely, this electrolysis is carried out in an electrolyzer incorporating an ion-conducting membrane that acts as a polymer electrolyte. Electrolyzers employing solid proton-conducting polymer electrolyte membranes or proton exchange membranes (PEMs) are called proton exchange membrane water electrolyzers (PEMWEs). Electrolyzers utilizing solid anion-conducting polymer electrolyte membranes or anion exchange membranes (AEMs) are called anion exchange membrane water electrolyzers (AEMWEs).

[0003] Catalyst-coated membranes (CCMs) can be used in the stacking of water electrolyzers. A CCM comprises an electrolyte membrane (such as a PEM or AEM) in which at least one of an anode catalyst layer and a cathode catalyst layer is coated onto the membrane surface. Typically, for PEMWEs, the cathode catalyst material includes platinum. The anode catalyst used for PEMWEs typically comprises iridium or iridium oxide (IrOx) materials or oxides containing both iridium and ruthenium.

[0004] To form a water electrolyzer, additional layers are added to either side of the CCM to create components, sometimes referred to as membrane electrode assemblies (MEAs). These additional layers may include a porous transport layer (PTL) on the anode side of the CCM and a gas diffusion layer (GDL) on the cathode side. These layers may or may not be directly attached to the CCM. Other components may include bipolar plates and current collector plates. Stacking such components constitutes an electrolyzer system that includes power and control systems.

[0005] Electrolyte membranes (such as PEM and AEM) are also used in fuel cells. In a proton exchange membrane fuel cell (PEMFC), the membrane is proton-conducting and transports protons generated at the anode across the membrane to the cathode, where they combine with oxygen to form water.

[0006] It is desirable to reduce the thickness of membranes used in electrochemical devices, such as water electrolyzers, to minimize electronic and ionic resistance. However, it is equally important to minimize any hydrogen permeation through the membrane to avoid hydrogen mixing with oxygen and the associated safety issues.

[0007] For water electrolyzers, it is beneficial to maintain low levels of hydrogen permeation even across the high pressure differential across the membrane. Using high pressure during electrolyzer operation is advantageous because it reduces the degree of compression required for the produced hydrogen and lowers operating costs. This has led to the use of membranes thicker than 125 µm, and often approaching 200 µm or more. Examples of membranes currently in use include Nafion. ™ N115 (125µm thickness) or Nafion ™ N117 (thickness 175µm).

[0008] Equally important is that the membrane remains stable during long-term electrochemical operation to minimize maintenance and replacement of expensive components.

[0009] It is known to coat membrane components with a catalyst layer (“composite catalyst”) suitable for catalyzing the recombination reaction of molecular oxygen and hydrogen.

[0010] For example, WO2018 / 115821A1 (Johnson Matthey Fuel Cells Ltd) describes a CCM having a laminated structure comprising a first layer, an intermediate layer, and a second layer. The intermediate layer is disposed between the first and second layers and has a composite catalyst layer disposed on its first surface. These layers can be combined by laminating a first membrane component, a second membrane component, and a third membrane component together.

[0011] Furthermore, WO2023 / 172626A1 (Electric Hydrogen Co) describes a composite layer placed outside the membrane (e.g., CCM) between a porous transport layer (PTL), such as... Figure 1 As shown.

[0012] It is also known to disperse the composite catalyst within the membrane itself rather than coating it onto the membrane component.

[0013] For example, WO2018 / 185615A1 (3M) describes a membrane for a water electrolyzer comprising at least one of metallic Pt or Pt oxide (as a composite catalyst), a cathode, and an anode. The composite catalyst can be incorporated into the membrane by adding a Pt-containing salt to the membrane followed by chemical reduction. Supported Pt can also be incorporated into the membrane by adding supported Pt pre-wetted with deionized water to a liquid suspension of an ionomer, followed by casting the resulting mixture into a membrane. Examples describe monolayer, bilayer, and trilayer membranes containing the composite catalyst. In the examples, bilayer and trilayer membranes are formed by lamination.

[0014] There is still a need to further enhance and develop membranes for electrochemical applications, such as water electrolysis, that can operate efficiently under high voltage differentials across the membrane. Summary of the Invention

[0015] The inventors have surprisingly discovered that thin electrolyte membranes with a thickness of 40 μm–60 μm can be produced with an excellent balance between low hydrogen permeability and high ionic conductivity. Such membranes can be produced by dispersing composite catalyst particles in a membrane layer of controlled thickness and forming the membrane as a single adherent membrane without lamination interfaces. These membranes are able to incorporate composite catalysts while maintaining high ionic conductivity.

[0016] Therefore, in a first aspect of the present invention, a bilayer electrolyte membrane is provided, the bilayer electrolyte membrane comprising:

[0017] A first layer comprising a polymer electrolyte having particles of a composite catalyst dispersed therein; and

[0018] The second layer comprises a polymer electrolyte without any composite catalyst dispersed therein; wherein

[0019] The thickness of the bilayer electrolyte membrane is 40µm-60µm;

[0020] The concentration of the composite catalyst in the first layer is 1 µg / cm³. 2 -100µg / cm 2 ;and

[0021] The bilayer electrolyte membrane is a single adherent polymer membrane.

[0022] These types of membranes are particularly suitable for use in water electrolyzers. Providing the membrane as a single, non-laminated component, rather than two or more membrane components laminated together, as described in WO2018 / 185615A1, also offers large-scale stability benefits and manufacturing process efficiency.

[0023] The membrane of the first aspect has a particular use as a component of a catalyst-coated membrane (CCM). It has been found that such CCMs provide an excellent balance between membrane resistance and low hydrogen permeation during operation. Therefore, in a second aspect of the invention, a CCM for an electrochemical device is provided, comprising the membrane according to the first aspect.

[0024] Suitablely, the CCM is used in a water electrolyzer, such as a PEM water electrolyzer. In such cases, the CCM includes a cathode catalyst layer for catalyzing the hydrogen evolution reaction and / or an anode catalyst layer for catalyzing the oxygen evolution reaction. Typically, the cathode catalyst layer contains platinum and / or the anode catalyst layer contains iridium.

[0025] This CCM can also be used in fuel cells, such as PEM fuel cells. In such cases, the CCM includes a cathode catalyst layer for catalyzing the oxygen reduction reaction and / or an anode catalyst layer for catalyzing the hydrogen oxidation reaction.

[0026] In a third aspect of the invention, a water electrolyzer or fuel cell is provided, the water electrolyzer or fuel cell comprising the membrane described in the first aspect or the catalyst-coated membrane described in the second aspect.

[0027] The inventors have also advantageously discovered that electrolyte membranes comprising the composite catalyst layer as described herein can be prepared by depositing a suitable ink rather than by lamination. Therefore, in a fourth aspect of the invention, a method for manufacturing a bilayer electrolyte membrane according to the first aspect is provided, the method comprising the steps of:

[0028] (ia) Apply an ink containing ionomers and without any composite catalyst dispersed therein to a substrate to form a precursor second layer;

[0029] (ii-a) Applying an ink containing an ionomer and having a composite catalyst dispersed therein to the second precursor layer to form the first precursor layer; or

[0030] (ib) An ink containing an ionomer and having a composite catalyst dispersed therein is applied to a substrate to form a precursor first layer;

[0031] (ii-b) Apply an ink containing an ionomer and without any composite catalyst dispersed therein to the first precursor layer to form a second precursor layer;

[0032] as well as

[0033] (iii) Dry the product of step (ii-a) or step (ii-b). Attached Figure Description

[0034] Figure 1 A schematic diagram of an exemplary arrangement of the electrolyte membrane of the present invention is shown.

[0035] Figure 2 A schematic diagram of an exemplary arrangement of a comparative catalyst-coated film not according to the present invention is shown.

[0036] Figure 3 The permeation degree (H2% in O2) of CCM 1 and CCM 2 prepared in the examples is shown. Detailed Implementation

[0037] Preferred and / or optional features of the invention will now be set forth. Any aspect of the invention may be combined with any other aspect of the invention unless the context otherwise requires. Any preferred and / or optional feature of any aspect may be combined with any aspect of the invention, alone or in combination, unless the context otherwise requires. Any subheadings are for convenience only and are not intended to limit the invention.

[0038] double membrane

[0039] The bilayer membrane described herein is particularly suitable as a proton exchange membrane (PEM), such as a PEM for water electrolyzers. However, those skilled in the art will understand that the layered structure described herein can be used for other types of electrolyte membranes, such as proton exchange membranes for fuel cells, and anion exchange membranes for water electrolyzers, fuel cells, or other applications.

[0040] The membrane is a bilayer electrolyte membrane, meaning that the only layers present are the first and second layers, which will be described more fully in later sections. Unless the context requires otherwise, references to "membrane" should be understood to mean a bilayer electrolyte membrane.

[0041] The membrane is a single adhesive polymer membrane. The term "adhesive" as used herein refers to a membrane without internal lamination interfaces.

[0042] The lamination of ion-conducting membranes involves pressing and / or bonding together at least two solid ion-conducting membranes, which may optionally be coated with a catalyst layer. A lamination interface is formed between the two membranes, wherein the solid surfaces of the individual membranes are pressed and / or bonded together. The lamination interface includes physical defects. Furthermore, the structure and / or chemical properties of the lamination interface differ from those of the host polymer material. This is because when a solid membrane is formed, the outer surface of the solid membrane has surface features that differ from those in the host material. For example, a hydrophobic surface layer is formed on the membrane surface at an air interface. Raman spectroscopy can detect this difference. Therefore, when two solid membranes are pressed together, the lamination interface formed by the two solid surfaces is chemically and / or structurally different from the host ion-conducting polymer material. Thus, microscopy and spectroscopic techniques can distinguish the lamination interface between ion-conducting polymer layers from interfaces formed via liquid-phase deposition processes such as printing, spraying, or layer coating to construct multilayer structures. That is, non-laminated interfaces differ structurally and / or chemically from laminated interfaces, and this difference is not merely a characteristic of the manufacturing method. Furthermore, in the absence of prior knowledge of the manufacturing process, a non-laminated interface can be identified as being non-laminated within the film. Examples of analytical techniques used to detect laminated interfaces include cross-sectional SEM. Changes in crystallinity at the interface can be detected using cross-sectional TEM. Other techniques used to detect laminated interfaces include 13C / 1H / 19F solid-state NMR, neutron diffraction, and / or combinations of two or more of the above techniques.

[0043] Such interfaces can increase the resistance of multilayer ion-conducting membranes due to physical defects and / or chemical changes at the lamination interfaces between ion-conducting polymer films. Therefore, it has been found advantageous to construct multilayer membrane structures by depositing ion-conducting polymer layers dispersed in a liquid solvent, rather than by laminating individual solid layers / films of ion-conducting polymers.

[0044] Although the membrane is a single adherent polymer membrane, the first and second layers can be distinguished in the cross-section of the membrane because the particles of the composite catalyst are dispersed in the first layer (and are therefore visible in the cross-section), but not in the second layer.

[0045] The membrane has a total thickness of 40 μm to 60 μm. Preferably, the membrane has a total thickness of 45 μm to 55 μm. Despite the relatively low thickness, hydrogen permeation remains low due to the arrangement of a composite catalyst within the membrane.

[0046] The membrane thickness (specifically, the thickness of the first and second layers) can be measured using scanning electron microscopy (SEM). The thickness of the first and second layers is calculated as the distance from one facet of the layer to the boundary between the first and second layers. SEM analysis is performed on a cross-section of the membrane, and the membrane and / or layer thicknesses are measured at multiple (e.g., 10) points. The thickness value is then determined by calculating the arithmetic mean of the measurements.

[0047] First layer

[0048] The first layer (also referred to as the "composite catalyst layer") is a membrane containing particles of a composite catalyst dispersed in an ion-conducting polymer. A composite catalyst is a catalyst that catalyzes the reaction between hydrogen and oxygen to form water. Therefore, the composite catalyst can be any catalyst capable of catalyzing the reaction between hydrogen and oxygen to form water, thereby reducing or preventing the permeation of hydrogen or oxygen, or both, through the membrane. Suitably, the composite catalyst is selected from one or more of platinum, palladium, and their alloys or mixed oxides. Preferably, the composite catalyst is platinum or a platinum alloy, such as platinum alloyed with one or more other platinum group metals (i.e., the element group including platinum, palladium, iridium, rhodium, ruthenium, and osmium) or platinum alloyed with cobalt. Particularly preferred is that the particles of the composite catalyst are composed of platinum.

[0049] Composite catalysts can be supported or unsupported, preferably unsupported. The term "unsupported" will be readily understood by those skilled in the art. For example, it should be understood that the catalyst particles are not bound or immobilized to a catalyst support (such as a carbon support) by physical or chemical bonds (e.g., by ionic or covalent bonds) or by nonspecific interactions (such as van der Waals forces). It has been found that the use of unsupported composite catalysts is beneficial for ink treatment prior to film formation and provides increased film stability during electrochemical operation, thereby avoiding degradation pathways via corrosion of the catalyst support.

[0050] When the membrane is used in a PEM electrochemical device, the ion-conducting polymer is suitably a proton-conducting polymer, and particularly a partially fluorinated or fully fluorinated sulfonic acid polymer. Examples of suitable proton-conducting polymers include perfluorosulfonic acid (PFSA) polymers, such as those available from 3M Corporation, or Aquivion (RTM) ion-conducting polymers available from Solvay. Preferably, the ion-conducting polymer is a PFSA polymer and has an equivalent weight in the range of 350 EW to 1200 EW and including end values ​​such as 600 EW to 1000 EW, and such as 700 EW to 900 EW. Preferably, the equivalent mass of the ion-conducting polymer in the composite catalyst layer is greater than the equivalent mass of the ion-conducting polymer in any other layer of the membrane. Preferably, the ion-conducting polymer in the second layer is the same as the ion-conducting polymer in the first layer. Alternatively, it is preferable that the ion-conducting polymers in the first and second layers are different.

[0051] "Dispersed in ion-conducting polymers" in this paper means that the particles of the composite catalyst are distributed throughout the composite catalyst layer, i.e., they are not located in discrete layers or regions of the composite catalyst layer.

[0052] Composite catalyst

[0053] Preferably, the composite catalyst particles have a particle size distribution such that d90 is less than or equal to 3.0 μm. Using particles with d90 less than or equal to 3.0 μm provides improved mechanical stability in thin film layers (such as layers with a thickness of less than 30 μm) and provides benefits associated with ink processability and ink use in coating equipment. The term "d90" as used in relation to particle size distribution in a membrane refers to the number distribution of particle size (the particle size value at 90% of the cumulative number distribution, i.e., 90% of the total particles in the sample have a diameter smaller than this value). The d90 of particles in a membrane can be determined by scanning electron microscopy (SEM), for example by analyzing the cross-section of the membrane by SEM, measuring the diameter of a particle group (e.g., 100 particles) based on the resulting image through image analysis, and then calculating the d90.

[0054] Preferably, the d90 is less than or equal to 2.8 μm, 2.6 μm, 2.5 μm, 2.4 μm, 2.3 μm, 2.2 μm, 2.1 μm, or 2.0 μm. Preferably, the composite catalyst particles have a particle size distribution such that the d90 is greater than or equal to 1.0 μm, 1.5 μm, 1.7 μm, or 1.9 μm. More preferably, the composite catalyst particles have a particle size distribution such that the d90 is in the range of 1.0 μm to 3.0 μm or 1.5 μm to 3.0 μm and includes end values, such as 1.5 μm to 2.8 μm or 1.5 μm to 2.6 μm.

[0055] Preferably, the composite catalyst particles have an average particle size greater than or equal to 0.1 μm. This average particle size can be determined by scanning electron microscopy (SEM), for example by analyzing the cross-section of the membrane with SEM and measuring the diameter of the observable particle group (e.g., 100 particles) through image analysis based on the resulting image, and then calculating the average (mean) particle size. Using particles larger than 0.1 mm provides advantages for efficient ink preparation and has been shown to provide a significant reduction in hydrogen permeation.

[0056] Preferably, the average particle size is greater than or equal to 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 μm, 0.7 μm, 0.8 μm, or 0.9 μm. Preferably, the composite catalyst particles have an average particle size less than or equal to 2.0 μm, 1.8 μm, 1.6 μm, 1.5 μm, 1.4 μm, 1.3 μm, or 1.2 μm. Preferably, the composite catalyst particles have an average particle size in the range of 0.2 μm to 2.0 μm, 0.5 μm to 2.0 μm, and including extreme values ​​such as 0.7 μm to 1.8 μm or 0.8 μm to 1.5 μm.

[0057] Composite catalysts can be supported or unsupported. Preferred characteristics of particle size distribution and average particle size apply to both supported and unsupported composite catalyst particles.

[0058] The first layer has a concentration of 1µg / cm 2 -100µg / cm 2 Within the range, preferably within 5µg / cm 2 -50µg / cm 2 More preferably within the range of 30 µg / cm 2 -50µg / cm 2 The range of composite catalyst loadings (e.g., platinum loading) has been found to provide a suitable balance between reducing hydrogen permeation levels during use and the associated costs of containing the catalyst in the membrane. Catalyst loading can be determined by inductively coupled plasma mass spectrometry (ICP-MS).

[0059] The composite catalyst layer preferably has a thickness in the range of 10 μm to 30 μm. The dispersion of composite catalyst particles in a 10 μm to 30 μm membrane layer provides improved membrane stability benefits compared to using a thinner catalyst layer (e.g., a catalyst layer applied to the membrane surface as described in WO2018 / 185615A1). The use of composite catalyst layers thicker than 30 mm does not require significant reduction in hydrogen permeation and may introduce manufacturing difficulties, especially when forming non-laminated membrane structures. The thickness of the composite catalyst layer can be determined by SEM analysis of the membrane cross-section. Preferably, the composite catalyst layer has a thickness in the range of 15 μm to 25 μm. This thickness provides a suitable balance between reducing hydrogen permeation through the formed membrane and manufacturing efficiency.

[0060] Preferably, the thickness of the first layer (composite catalyst layer) is less than the thickness of the second layer (without composite catalyst). This asymmetry means that the composite catalyst is placed closer to the anode than the cathode in a water electrolyzer configuration, which is believed to help reduce hydrogen permeation.

[0061] Second floor

[0062] Preferably, the second ion-conducting polymer layer has a thickness in the range of 20 μm to 40 μm, such as in the range of 25 μm to 35 μm.

[0063] Preferably, the membrane contains a reinforcing polymer, such as expanded polytetrafluoroethylene (ePTFE) or polybenzimidazole (PBI). The first and / or second layers may contain the reinforcing polymer, and preferably, the second layer contains the reinforcing polymer. Particularly preferred is that the second layer contains the reinforcing polymer, and the first layer does not contain the reinforcing polymer. In the presence of the reinforcing polymer, it is not considered a separate layer, but rather a component of the first or second layer. The reinforcing material may comprise a porous reinforcing polymer sheet impregnated with an ion-conducting polymer, optionally expanded polytetrafluoroethylene (ePTFE). Since typical reinforcing polymer materials are not ion-conducting, or only adequately ion-conducting, porous reinforcing polymers are used to form the reinforcing layer, which utilizes the pores of the material to impregnate it with an ion-conducting polymer to provide an ion conduction path from one side of the layer to the other.

[0064] Preferred features of membrane

[0065] Preferably, the membrane contains a radical reducing additive (e.g., a peroxide radical reducing additive, such as a cerium-containing compound, such as a cerium salt or cerium oxide (CeO2)). It should be noted that peroxides can decompose to form a series of free radicals (O, OH, OOH), and the radical reducing additive can reduce the amount of one, several, or all of these free radicals. For the avoidance of doubt, the radical reducing additive is a separate component from the composite catalyst. When present, it is preferable that the radical reducing additive is dispersed within the composite catalyst layer. In some embodiments, the membrane does not contain a radical reducing additive.

[0066] The thickness of the ion-conducting polymer layer can be adjusted, for example, by changing the number of deposition steps of the ion-conducting polymer during the membrane manufacturing process, or by changing the pump speed during the deposition of the ion-conducting polymer.

[0067] In a preferred embodiment, the bilayer membrane comprises or consists of: (i) a first layer having particles of a composite catalyst dispersed therein and having a thickness of 10 μm-30 μm; and (ii) a second layer having a thickness in the range of 20 μm-40 μm; wherein the thickness of the bilayer electrolyte membrane is 40 μm-60 μm, and the concentration of the composite catalyst (such as platinum) in the first layer is 1 µg / cm³. 2 -100µg / cm 2 Furthermore, the bilayer electrolyte membrane is a single adherent polymer membrane. In this configuration, it is preferable that the second layer comprises a reinforcing polymer, such as expanded polytetrafluoroethylene (ePTFE) or polybenzimidazole (PBI). This membrane structure has been found to provide a particularly suitable balance between membrane resistance and hydrogen permeation level.

[0068] Catalyst Coated Film

[0069] The membranes described herein can be suitably used as part of a catalyst-coated membrane (CCM). Such CCMs have an anodic catalyst layer and / or a cathode catalyst layer applied to the surface of the membrane.

[0070] Cathode catalyst layer

[0071] In the case of a CCM used in a water electrolyzer, a cathode catalyst layer can be applied to the surface of a membrane containing a catalyst for catalyzing the hydrogen evolution reaction. Preferably, the cathode catalyst layer contains platinum, such as a carbon-supported platinum catalyst. The catalyst material can be formulated as an ink, non-in-situ printed onto a PTFE sheet, and transferred onto the membrane by hot pressing. Alternatively, the ink can be directly coated onto the membrane.

[0072] Preferably, the cathode catalyst layer comprises platinum and has a content of less than 1 mg provided by a platinum material (such as a carbon-supported platinum material).Pt cm -2 The platinum loading must be within a certain limit. In other words, there is a lower limit to the amount of platinum that must be provided. Therefore, the platinum loading of the cathode layer should appropriately be greater than 0.01 mg. Pt cm -2 0.04mg Pt cm -2 Or 0.06mg Pt cm -2 .

[0073] The cathode catalyst layer may comprise a carbon-supported platinum catalyst material, wherein the platinum supported catalyst material is between 20 wt% and 60 wt% platinum, optionally between 40 wt% and 60 wt% platinum. Platinum is advantageously provided as nanoparticles on the carbon support material. The platinum nanoparticles may have the following crystallite sizes: at least 1 nm, 2 nm, or 3 nm; not exceeding 15 nm, 10 nm, or 6 nm; or within any combination of the lower and upper limits described above. The crystallite size can be measured by XRD and fitted using Rietveld analysis. X-ray diffraction data were collected on a Bruker AXS D8 using Cu Kα radiation (λ = 1.5406 Å and 1.54439 Å). The crystallite size was calculated and refined using the LVol-IB method by Rietveld.

[0074] The cathode catalyst layer may comprise a carbon-supported platinum catalyst material, wherein the carbon support material is a partially graphitized carbon material (e.g., heat-treated carbon black). Graphite materials are more corrosion-resistant. However, graphite support materials have a low surface area. Therefore, there is a trade-off between the requirements of high surface area and high corrosion resistance. Partially graphitized materials have been found to offer a good compromise between the surface area requirements and corrosion resistance requirements of carbon supports in this water electrolyzer application.

[0075] Typically, the cathode catalyst layer comprises both a catalyst and an ion-conducting polymer. The ion-conducting polymer in the cathode catalyst layer can be an ionomer, such as a perfluorosulfonic acid (PFSA) polymer. The ion-conducting polymer in the cathode layer can be the same as or similar to the ion-conducting polymer used in the membrane.

[0076] The cathode catalyst layer may have an ion-conducting polymer / carbon weight ratio in the range of 0.6 to 1.0 and including the end value (note that this is the weight ratio between the ion-conducting polymer and carbon, and platinum is not considered in this calculation). Furthermore, the cathode catalyst layer may have a thickness in the range of any one of 1 μm to 15 μm, 4 μm to 15 μm, or 8 μm to 15 μm.

[0077] Examples of such cathode layers include the following characteristics:

[0078] -Nominal Pt loading—0.4 mg Pt cm-2

[0079] -Ion-conducting polymer—ionomer 800EW 3M C4 side chain

[0080] -Ion-conducting polymer / carbon weight ratio—0.8

[0081] -Thickness—Approximately 10μm to 11μm

[0082] -The catalyst is 50% by weight of carbon-supported platinum.

[0083] - Carbon is a partially graphitized carbon support material.

[0084] Anode catalyst layer

[0085] In the case of a CCM used in a water electrolyzer, an anode catalyst layer can be applied to the surface of a membrane containing a catalyst for catalyzing the oxygen evolution reaction. In the case of a CCM used in a PEMWE, it is preferable that the anode catalyst layer contains iridium, such as iridium oxide or a mixed oxide of iridium with one or more other metals.

[0086] The anode material can be formulated into an ink, appropriately in an ion-conducting polymer, and non-in-situ printed onto a PTFE sheet, and then transferred onto a membrane by hot pressing. Alternatively, the ink can be directly coated onto the membrane.

[0087] The anode catalyst layer typically contains both a catalyst and an ion-conducting polymer.

[0088] The anode catalyst layer may comprise between 5% and 20% by weight, for example, between 8% and 15% by weight, an ion-conducting polymer. Suitably, the amount of catalyst material in the anode catalyst layer may be between 80% and 95% by weight, optionally between 85% and 92% by weight. The iridium loading of the anode catalyst layer is preferably less than 3 mg Ir / cm³. 2 Optionally at 0.05 mg Ir / cm 2 and 3mg Ir / cm 2 Within the range. The iridium-containing catalyst material can be an iridium oxide catalyst material, and the anode catalyst layer can have a thickness between 6 μm and 15 μm.

[0089] Preferably, the anode catalyst layer is adjacent to the first layer (containing a composite catalyst).

[0090] Manufacturing method

[0091] A method for manufacturing the electrolyte membrane as described above is also provided, the method comprising the following steps:

[0092] (ia) Apply an ink containing ionomers and without any composite catalyst dispersed therein to a substrate to form a precursor second layer;

[0093] (ii-a) Applying an ink containing an ionomer and having a composite catalyst dispersed therein to the second precursor layer to form the first precursor layer; or

[0094] (ib) An ink containing an ionomer and having a composite catalyst dispersed therein is applied to a substrate to form a precursor first layer;

[0095] (ii-b) Apply an ink containing an ionomer and without any composite catalyst dispersed therein to the first precursor layer to form a second precursor layer;

[0096] as well as

[0097] (iii) Dry the product of step (ii-a) or step (ii-b).

[0098] The term “first precursor layer / second precursor layer” is used to refer to the layer that eventually becomes the first layer / second layer after step (iii).

[0099] The method includes performing steps (ia), (ii-a), and (iii) sequentially, or steps (ib), (ii-b), and (iii). When steps (ia) and (ii-a) are followed, a second precursor layer is applied to the substrate before the first precursor layer. When steps (ib) and (ii-b) are followed, a first precursor layer is applied to the substrate before the second precursor layer.

[0100] Preferably, the method includes steps (ia), (ii-a), and (iii). This sequence is more suitable for incorporating the reinforcing agent into the second layer of the precursor. In a preferred embodiment, the method includes an additional step of adding the reinforcing agent to the second layer of the precursor, performed after step (ia) and before step (ii-a). In this way, the reinforcing agent is incorporated into the second layer of the precursor.

[0101] The drying step may preferably be performed after step (ia) or step (ib). It may also preferably be performed after step (ii-a) or step (ii-b). Any drying step performed between steps (i) and (ii) and between steps (ii) and (iii) should be sufficient to remove some or all of the solvent, but should not be hot enough to cause annealing. A person skilled in the art will be able to determine the appropriate temperature and duration for the drying step.

[0102] When the composite catalyst particles are platinum particles, it is preferable to provide the platinum particles in the form of platinum black. It has been found that platinum black can be efficiently processed to provide inks suitable for use in methods as described herein, and exhibits less agglomeration during ink formation than other platinum sources, such as carbon-supported platinum.

[0103] Preferably, the composite catalyst particles in the ink have a d90 of less than 3.0 μm. The particle size distribution can be determined using laser diffraction. For example, d90 can be determined by diluting the ink with an 80:20 (v / v) ethanol:water mixture and analyzing the particle size distribution by laser diffraction, such as using a Malvern Mastersizer 3000. The term "d90" in relation to particles in ink refers to volume-based particle size (the particle diameter value at 90% of the cumulative volume distribution, i.e., 90% by volume of the particles in the sample have a diameter smaller than this value).

[0104] The desired particle size distribution can be appropriately achieved by processing the ink using high-shear techniques such as microfluidization. Preferably, forming the ink involves passing a dispersion of a platinum source (such as platinum black) and an ion-conducting polymer through a microfluidizer.

[0105] Inks typically comprise ion-conducting polymers dispersed in a solvent. The solvent can be a mixture of an organic solvent and water. For example, the solvent can be a mixture of an alcohol (such as ethanol or propanol) and water. The volume ratio of the organic solvent (such as ethanol) to water can be: at least 60:40, 70:30, or 75:25; not exceeding 95:5; 90:10 or 85:15; or within any combination of the lower and upper limits described above. The solvent is formulated to achieve desired dispersion, coating, and drying characteristics.

[0106] The ion-conducting polymer may be provided in the ink in the following weight percentages relative to the total weight of the composite catalyst and the ion-conducting polymer: at least 7 wt%, 10 wt%, 14 wt%, or 16 wt%; not exceeding 22 wt%, 20 wt%, or 18 wt%; or within any combination of the lower and upper limits described above. The ion-conducting polymer content is selected to achieve the desired dispersion, coating, and drying characteristics.

[0107] The ink may also contain free radical reducing additives (e.g., peroxide free radical reducing additives, such as cerium dioxide). For example, the free radical reducing additive may be provided in the dispersion in weight percentages relative to the weight of the ion-conducting polymer as follows: at least 0.15 wt%, 0.20 wt%, or 0.23 wt%; not exceeding 0.35 wt%, 0.30 wt%, or 0.28 wt%; or within any combination of the lower and upper limits described above.

[0108] The ink can be applied in steps (i) and (ii) by any suitable method, but is typically done by casting or printing the ink onto the substrate to form a layer.

[0109] The membrane structure described above can be coated with both a cathode and an anode catalyst to form a catalyst-coated membrane (CCM) for a water electrolyzer. The specific types of catalysts used for the cathode and anode can vary. Furthermore, the deposition method can also vary. An example of a suitable cathode catalyst for a water electrolyzer is a carbon-supported platinum catalyst, optionally provided in decal form. In the case of a CCM for a PEMWE, an iridium oxide-based catalyst can be used for the anode. The iridium oxide-based catalyst can be prepared as an ink comprising an ion-conducting polymer, 1-propanol, and water, and rod-coated onto a Teflon sheet and dried to form a decal. The catalyst decal can be hot-pressed together with the membrane to form the CCM.

[0110] The present invention will now be described with reference to the following embodiments. These embodiments are provided to aid in understanding the invention and not to limit its scope.

[0111] Example

[0112] Ink formation

[0113] The ion-conducting polymer dispersion is produced by mixing an ion-conducting polymer (PFSA ionomer, 825EW, 3M Advanced Materials) with water and ethanol (approximately 20:80). A second dispersion of free radical scavenging additive (cerium dioxide), water, and ethanol is metered into this dispersion to achieve a target amount of free radical scavenger (approximately 0.3% by weight relative to the weight of the ionomer). This is referred to below as the first ink.

[0114] A granular platinum black catalyst (Johnson Matthey plc) was added to a mixture of an ion-conducting polymer (PFSA ionomer, 825EW, 3M Advanced Materials) and water. The mixture was induced to flow at 30,000 psi using a Z-chamber microfluidicator (Microfluidics M-110P) until a noticeable decrease in the ink viscosity was observed. A second ink was prepared by adding a certain amount of platinum catalyst dispersion to the first ink, adjusting the amount of platinum to achieve 30 µg / cm³. 2 The target Pt load.

[0115] Formation of a 50-μm bilayer proton exchange membrane (E1)

[0116] Preparation with Figure 1 The illustrated double-layer membrane has a layered structure. The double-layer membrane includes the following components:

[0117] Contains a concentration of 30 µg / cm 2 The composite catalyst has a layer approximately 21.0 µm thick, known as the "first layer";

[0118] A layer approximately 28.5 µm thick containing reinforcing agents but no composite catalysts, referred to as the "second layer".

[0119] The bilayer film is prepared as follows. A first ink is applied to the substrate using a slit-die coating process to form a Pt-free layer (“second layer”) containing ePTFE reinforcing agent, and then dried in an oven to remove the solvent.

[0120] The second ink was applied onto the second layer in the same manner to form a Pt-containing layer (“first layer”) and then dried in an oven to remove the solvent.

[0121] Then the entire membrane is annealed.

[0122] Formation of a three-layer 50-μm proton exchange membrane (CE2)

[0123] Preparation with Figure 2 The double-layer membrane with the layered structure shown is an example. A triple-layer membrane includes the following:

[0124] A layer approximately 10.5 µm thick without any composite catalysts or reinforcing agents, the “first layer”;

[0125] A layer approximately 10.5 µm thick containing a Pt composite catalyst at a concentration of 30 µg / cm, referred to as the "second layer";

[0126] A layer approximately 28.5 µm thick containing reinforcing agents but no composite catalysts, known as the "third layer".

[0127] The three-layer film was prepared as described above, except that the platinum-containing dispersion used to prepare the second layer had twice the platinum concentration and was coated to a thickness of half, achieving the same platinum loading. Following this, the first layer was applied using the first ink.

[0128] Measurement of film thickness and layer thickness

[0129] Two membrane specimens (approximately 2 × 1 cm) were taken from different locations on the membrane sample. The specimens were embedded in epoxy resin and cured overnight at room temperature. The blocks were then ground, polished, and coated with carbon.

[0130] The cross-sections of each sample were then analyzed at 2-3 locations using scanning electron microscopy (SEM), and the film thickness and layer thickness were measured based on the SEM images. The arithmetic mean of the film thickness and / or layer thickness was then calculated from the measurement results (approximately 10 measurements for each thickness parameter).

[0131] Preparation of CCM

[0132] CCM 1 and 2 consist of a cathode catalyst layer with Pt / C-PFSA ionomer (with 0.4 mg cm⁻¹). -2 The Pt loading of Pt) and the IrOx-PFSA ionomer anode catalyst layer (with 1.4 mg cm⁻¹) -2 Membranes E1 (bilayer) and CE2 (trilayer) with Ir loading were prepared, with the anode layer applied to the membrane layer containing the composite catalyst.

[0133] CCM performance test

[0134] Hydrogen permeation

[0135] The hydrogen permeation level of each CCM was measured at different current densities using the following method. A water electrolysis cell with a catalyst-coated membrane to be tested was prepared. The cell temperature was maintained at 80°C, and the anode and cathode pressures were set to 2 bar and 6 bar, respectively. Then, the current density was set to 3 A / cm². 2 And maintain it for 2.5 hours. Then set the current density to 2 A / cm². 2 And continue for 2 hours, then 1A / cm 2 And continue for 2.5 hours, then 0.5 A / cm 2 And it lasted for 4.5 hours. The H2 in the oxygen at the anode gas outlet was measured using a sensor that measures thermal conductivity.

[0136] Electrical performance

[0137] The electrical performance of the CCM was tested using the following method. First, the CCM was conditioned at 80°C for 12 hours with water flowing through the anode. Then, polarization measurements were performed. The anode and cathode pressures were kept equal at 0 bar. The current density was 0.04 A / cm². 2 The step size starts from 0 A / cm 2 Increased to 1A / cm 2 And then at 0.08 A / cm 2 The step size is from 1A / cm 2 Increased to 4A / cm 2 Then, the current density was set at 0.08 A / cm². 2 The step size is from 4A / cm 2 Reduced to 1A / cm 2 And then at 0.04 A / cm 2 The step size is from 1A / cm 2 Reduced to 0A / cm 2 Measurements taken from low to high current were used for further analysis. The results are shown in Table 1.

[0138]

[0139] Table 1 .

[0140] Figure 3 The H2% in O2 as a function of current density is shown for CCMs 1 and 2. H2% in O2 is an indicator of the degree of hydrogen permeation. CCM1 shows significantly lower H2 permeation compared to CCM2. Both CCMs exhibit low resistivity consistent with the structure of a single adhered polymer membrane.

Claims

1. A bilayer electrolyte membrane comprising: a first layer comprising a polymer electrolyte having particles of composite catalyst dispersed therein; and a second layer comprising a polymer electrolyte having no composite catalyst dispersed therein; wherein the bilayer electrolyte membrane has a thickness of 40 pm - 60 pm; The concentration of the composite catalyst in the first layer is 1 µg / cm 2 - 100 µg / cm 2 ; and the bilayer electrolyte membrane is a single adhered polymer membrane.

2. The bilayer electrolyte membrane of claim 1, wherein the composite catalyst is selected from one or more of platinum, palladium, and alloys or mixed oxides thereof.

3. The bilayer electrolyte membrane of any one of claims 1 to 2, wherein the first layer has a thickness of 10 pm - 30 pm.

4. The bilayer electrolyte membrane of any one of claims 1 to 3, wherein the first layer has a thickness of 15 pm - 25 pm.

5. The bilayer electrolyte membrane of any one of claims 1 to 4, wherein the second layer has a thickness of 20 pm - 40 pm.

6. The bilayer electrolyte membrane of any one of claims 1 to 5, wherein the second layer has a thickness of 25 pm - 35 pm.

7. The bilayer electrolyte membrane of any one of claims 1 to 6, wherein the bilayer electrolyte membrane has a thickness of 45 pm - 55 pm.

8. The bilayer electrolyte membrane according to any one of claims 1 to 7, wherein the concentration of the composite catalyst in the first layer is 5 µg / cm 2 to 50 µg / cm 2 .

9. The bilayer electrolyte membrane according to any one of claims 1 to 8, wherein the concentration of the composite catalyst in the first layer is 30 µg / cm 2 - 50 µg / cm 2 .

10. The bilayer electrolyte membrane of any one of claims 1 to 9, wherein the first layer and / or the second layer contains a reinforcing polymer.

11. The bilayer electrolyte membrane of claim 10, wherein the second layer contains a reinforcing polymer and the first layer does not contain a reinforcing polymer.

12. The bilayer electrolyte membrane of any one of claims 1 to 11, wherein the first layer has a thickness that is less than the thickness of the second layer.

13. A catalyst coated membrane for an electrochemical device, the catalyst coated membrane comprising the bilayer electrolyte membrane of any one of claims 1 to 12.

14. A fuel cell or water electrolyzer comprising the membrane of any one of claims 1 to 12 or the catalyst coated membrane of claim 13.

15. A method of manufacturing the bilayer electrolyte membrane of any one of claims 1 to 12, the method comprising the steps of: (i-a) applying an ink comprising an ionomer and having no composite catalyst dispersed therein to a substrate to form a precursor second layer; (ii-a) applying an ink comprising an ionomer and having composite catalyst dispersed therein to the precursor second layer to form a precursor first layer; or (i-b) applying an ink comprising an ionomer and having composite catalyst dispersed therein to a substrate to form a precursor first layer; (ii-b) applying an ink comprising an ionomer and having no composite catalyst dispersed therein to the precursor first layer to form a precursor second layer; and (iii) drying the product of step (ii-a) or step (ii-b). ​ 16. The method according to claim 15, comprising steps (i-a) and (ii-a) and an additional step of adding a reinforcing agent to the precursor second layer after step (i-a) and before step (ii-a).

17. The method according to claim 15 or claim 16, wherein the drying step is performed after step (i-a) or step (i-b).

18. The method according to any one of claims 15 to 17, wherein the drying step is performed after step (ii-a) or step (ii-b).

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